The invention relates to a method and apparatus for obtaining an acceleration or deceleration signal from a signal proportional to speed, wherein at successive times, adjacent times being at a constant interval .DELTA.T from one another, the change in the speed signal is ascertained with respect to the speed signal present at the foregoing time and the acceleration or deceleration signal is obtained by means of addition of a predetermined number of successive changes.
A method for obtaining the acceleration or deceleration is known from the German laid-open application No. 24 38 273. There, at successive measuring times of equal intervals .DELTA.T apart, a stored digital speed signal is compared with the newly ascertained digital speed signal and the difference is furthermore filtered in order to eliminate interference. Subsequently, the filtered signals are added up until a predetermined period has elapsed. If during this period a predetermined threshold is not exceeded, then the period begins over again. If in the course of a period the threshold is exceeded, then a switching signal indicating the exceeding of an acceleration or deceleration threshold is generated; the period then immediately begins over again. In this laid-open application, it is also disclosed that the periods can be shortened and the threshold can be lowered, in order to be able to suppress the switching signal again immediately, upon a corresponding change in the course of acceleration or deceleration.
A method is also known from the German laid-open application No. 23 42 358 of storing the signal corresponding to a speed at the beginning of a measurement period and comparing this signal with the continuously ascertained signal corresponding to speed. If during the measurement period a predetermined threshold is not exceeded as a result of the difference, then a new measurement period begins upon the end of the foregoing period. If the threshold is exceeded during the period, then a switchover is made immediately to a new beginning of a period, the switching signal is generated, and if needed the measurement period is shortened and the threshold is lowered.
In both methods and their attending apparatus, it can happen or occur that the threshold is almost attained at the end of a measurement period. Despite this, a new measurement period begins and the difference, or the sum of the difference values, must be generated again from zero, until they exceed the threshold. Thus, in these methods, it may happen that the switching signal is generated quite belatedly, with its generation depending on the coincidental relationship between the phase position of the measurement period and the course of the acceleration or deceleration. Shortening the measurement period after a first occurrence of exceeding the threshold is intended to counteract this possible delay in the signal generation. When the switching signal is used in a control loop, for instance an anti-locking control system, this delay can have quite deleterious effects.